Jeffrey LewisIs North Korea Pursuing Boosted Bombs?


Over at 38 North, I have a post up about North Korea’s boast that its scientists “succeeded in nuclear fusion reaction” and what that might mean for its stockpile of nuclear weapons:

A boosted weapon requires tritium (or, in the case of the “layer cake,” lithium-6 deuteride) which has a half-life of only 12.4 years and must be produced in a nuclear reactor. Did North Korea produce a small amount of tritium in one of its reactors or purchase the material from Pakistan? There is no public confirmation—or even as far as I know defector allegations—that North Korea is developing a boosted fission weapon or stockpiling tritium, lithium-6 deuteride or other fusion fuels. If it is a reasonable assumption that boosted weapons are North Korea’s next step, there is no solid evidence that they have taken it—yet.

Am looking forward to the comments on this one.


  1. Seb (History)

    Speaking as a fusion scientist, I think you may be barking up the wrong tree with Tokamaks.

    Even small ones capeable of doing fusion tend to be expensive and require a lot of effort to keep working, and it is difficult to see what on earth they would learn that was weapons related.

    As for using a DT mix in a tokamak, which you mentioned in the 38North post, the main reason for not doing it is less about upsetting the neigbours and more that Tokamaks tend to need a lot of tinkering. Playing with tritium is expensive and complicated, and often not necessary for the science involved, so you don’t generally bother unless you want to study how the products of the fusion reaction behave inside the reactor (high energy alpha particles) and to check that what you think ought to happen based on DD plasmas does actually happen in DT plasmas. Again, I am not sure why you would bother if you were North Korea, H-bomb plasmas are very different to what you would get in a Tokamak.

    ICF is a more obvious candidate for weapons related activity. H bombs are in fact a form of inertial confinement, instead of lasers you are using xrays generated from stuff heated up by an A bomb.Cynics might point out one of the reason so much money is spent on ICF is the interest in testing simulation codes of radiation driven implosion of solid density plasmas being of some interest to nuclear weapons labs. But I would think this is way out of NK’s league.

    As for NK doing fusion, well, I would imagine that the simplest way to get fusion reactions would be from electrostatic confinement, using electric fields to squash deuterium atoms together. This can be done with a few thousand dollars. Problem is that it does not scale to making power, but it can make a compact neutron source. All in all: MCF seems unlikely (particularly putting tritium into them) due to complexity and lack of relevance. ICF might be relevant to weapons, but is highly challenging, and thus unlikely. Electrostatic fusors are essentially harmless, but allows you to say you are doing fusion. It may have some application as a neutron source though.

  2. Steven Dolley (History)

    I don’t think anyone’s seriously suggesting that the DPRK has developed fusion reactors of any design. The discussion of tritium in the post is limited to its potential use in boosting the yield of nuclear fission weapons.

  3. Azr@el (History)

    Yes, North Korea is probably “Pursuing Boosted Bombs” and No, this has nothing to do with it. Most “probably” a small lab is burning deuterium either with a DPF, a fusor($2k), maybe a pyroelectric setup($300) etc… And maybe someone over there believes that will lead to clean, cheap and abundant energy…god knows we have the same crowd of kooks here. Or maybe they’re using it for basic education in the field of plasma physics. And as a wild card I wouldn’t too quickly dismiss the outside chance of a North Korean MCF program; I know the Iranians have a tokamak, maybe the DPRK have one as well?

  4. FSB

    A small experimental neutron trigger device is consistent with all statements on the matter — and it is not a huge deal. Everything nuk-ku-ler at the axis of evil is not a cause for concern or speculative extrapolations.

  5. George William Herbert (History)

    I believe i’ve gone on the record several times that the posited 4kt target yield for the NK bomb only makes military sense as the unboosted yield of a design intended to boost (to much higher yields), fired without “live” boost gas (D-T mixture) to reduce test burial requirements and obscure final military yield.

    Note the “military sense” there – in terms of deterrence, 4 kt being waved at Tokyo or Seoul would be a very significant deterrent, even with the knowledge that a much larger weapon would do much more damage. So it’s entirely possible that they settled on 4 for strategic reasons, despite the fact that just about everyone else uses larger ones and that they could probably as well.

  6. Alex W. (History)

    There are, of course, reasons for making fusion neutrons that would be useful for a weapons program other than directly as part of the design itself. Chapter 12 of the Handbook for Notification of Exports to Iraq, Annex 3, for example has a nice entry on “Neutron Generator Systems That Use Dense Plasma,” wherein DT neutrons are used for “be used to develop, test, and benchmark neutron diagnostic equipment used in the development of nuclear weapons. It may also be used as a research tool for the study of weapons materials.” It strikes me as more likely than any of your three options, just because it would actually give you more information on future weapons design. Boosting without a constant supply of tritium seems difficult, since the tritium will decay into He3, which as I understand it is a strong neutron absorber.

    It seems unlikely to me that they would have either Tokamak or ICF style fusion programs — it seems rather unfathomable to me that they would be able to get more information out of their own fledgling efforts than they could just get out of the unclassified literature. MCF fusion has been declassified since 1958 and has a copious body of open literature about it (and plasma behavior, DT burn, etc.). ICF has been largely declassified since the early 1990s, and my understanding is that it’s really a round-about way to go about getting weapons data if you are not already an advanced weapons state with lots of weapons testing data to compare it to.

    Re: Seb — I don’t think just “cynics” would point out that the US ICF effort is largely weapons based. Even today, when a large part of the NIF publicity is about possible long-term energy benefits, LLNL still lists “stockpile stewardship” and “national security” as their #1 reason for existence. In fact, historically speaking, the US government has always been pretty straight-up about the fact that ICF in the short- and middle-term is more about weapons research than it is about clean energy (which may or may not be economical even if it is technically feasible). ICF is definitely relevant to weapons, but I doubt North Korea is doing ICF; it does not strike me as a very good investment for a very new nuclear state.

  7. anonymous (History)

    A high probability for for the second NK low yield shot is that it was a core for a boosted or worse, thermonuclear device. To assume rouge nations are too intellectually challenged to replicate 1940’s and 1950’s technology before the invention of the 16 gigaflop desktop (a 1980’s supercomputer equivalent) is just as “intellectually challenged”. Assuming that country X or country Y is Z years away from a 1950’s solution is an unacceptable risk. I am obviously extremely concerned.

  8. FSB

    or they are not very good at making complicated nuclear devices (anonymous’ comment notwithstanding) and 4kT is all they could coax out. They seem to also have trouble with their ICBM/space launch program, also 1950s technology.

    As Azr@el says there are more logical explanations regarding the hardware than a two stage boosted device.

  9. Seb (History)


    My point was more that an announcement about achieving fusion, assuming it has been done in any of the common ways in the civil sector, probably doesn’t tell us much about the shape of their programme.

    Though a 2k fusor neutron source might have applications.

    Well, the information point we are working off is that they have achieved fusion reactions.

    To get significant fusion reactions you need significant energy confinement times, which means a big Tokamak, with large power supplies and probably neutral beam injectors… such a facility would be large, easily detected, and require mastering a lot of different skills.

    A small MCF for basic plasma physics is easily achievable (I’m working on something similar to that in Costa Rica), but whether they are doing that or not, it wouldn’t result in an announcement like the one they made.

    Like you, I would guess if they are showboating about achieving fusion, an electrostatic confinement machine like a polywell or a fusor seems the most likely thing they would have done. It’s the simplest thing that shows any promise for controlled fusion reactions, and there are people in the west that are pursuing it even if most people think they will not scale.

    Unless there are other devices that are weapons components that involve fusion, as FSB suggests.

    @Alex W:
    I say cynic more in politeness to my colleagues in ICF. There are a lot of inertial confinement plasma physicists that are absolutely insistent that ICF is purely peaceful and get very upset when you point that connection out, both on moral grounds and at the implication that ICF as commercial power is not a promising line of research.

    NIF may be open about the weapons application, but the French laser facility is ostensible purely civil, and there is a planned UK facility that is supposed to be entirely pursuing high repetition rates etc. for commercialisation. Plus there is all the work that uses pinches.

    Personally, I wonder if there would be as much civil interest in ICF without the military funding. I know AWE used to send employees to study post graduate plasma physics at Imperial College in the UK, and I am sure they paid through the nose for it and are happy to do so if that money is being spent on people looking at laser driven plasmas, ICF theory and pinches for commercial power generation, thus keeping a body of knowledge, skills and tools available to support their own work.

  10. George William Herbert (History)

    Re FSB’s comment –

    Fusion boosting isn’t two-stage, it’s primary enhancement.

    It’s possible that they can’t do better. But that’s a highly questionable assumption, IMHO. Doing far better than that is not a difficult task, even within the physical size envelope their large missiles’ warheads require.

  11. bob (History)

    Remember that DPRK has an issue that most nuclear weapon states don’t face, namely that their principal target (Seoul) is in their own country (Korea). . .

    They too want reunification, albeit on their own terms.

    So the shock-and-awe of dumping a 4kt device over a specific suburb of Seoul may be used, in the wider context of a conventional invasion, as a showstopper to get an armistice at a time of their own choosing.

    The yield may be small but sufficient.

    Clearly, they add the pixie gas to the one bound for Japan.

  12. George William Herbert (History)

    Bob –

    IMHO, Seoul is most assuredly not the military target of record. For MAD deterrence purposes, all of Seoul, Tokyo, and to some lesser degree Beijing and Vladivostok would qualify, but them firing up Seoul in any significant way other than to avoid their own national extinction seems unlikely.

    On the other hand, I don’t spend my days trying to live inside their heads. So what do I know.

    In terms of military targets, the things they’re likely to want to actually nuke would be the big ports and airfields that US and other reinforcements would stream through in the event of a major war.

    Your specific scenario – using a nuke to get an armistice – is extremely unlikely. I can’t think of a US president who would not respond to that by reducing NK to a glowing hole in the ground. While one can negotiate an immediate armistice with a glowing hole in the ground, the utility of doing so seems somewhat pointless. I think NK knows that, or at least hope so.

  13. Josh (History)

    Consider the possibility that North Korea has no particular military doctrine for nuclear weapons, and simply wishes to be recognized as a “nuclear weapons state.”

  14. CB (History)

    I, for one, am deeply involved in an ICF project that is private and totally non-military. Strictly for commercial power. As to the NK’s, I go with GWH’s unboosted design as first choice and the the neutron trigger as second

  15. Seb (History)

    (Off topic, moderators, but I’ll leave it at this)
    CB: That’s interesting. I’d like to talk to someone more involved with commercial ICF power rather than just the narrow physics… it always seemed to me that the optimisim was getting to ignition easier than MCF, but then being left with some pretty hefty problems to commercialise. Not that MCF is particularly promissing either, frankly.
    Would you be willing to exchange a few emails?

  16. Bruce Klingner (History)

    South Korea media reported detection of xenon after North Korea’s claimed fusion experiment (Radioactivity Detected After N.Korea Nuclear Fusion Claim,

    Could any of the many technical experts here comment on whether that makes Pyongyang’s claim any more likely?

  17. Roger (History)

    What is a BOOSTED BOMB?

    You mean a Thermonuclear weapon or a Hydrogen bomb.

    Don’t invent words like “Boosted Bomb”

  18. Helian (History)

    Roger, a boosted bomb is one in which the yield of the primary, or fission part, is “boosted” with the aid of fusion reactions. Boosting is not associated with the thermonuclear, or secondary part of the weapon, for which the primary serves as a trigger. As for ICF, its scientific feasibility was confirmed in nuclear tests. However, in the US, almost all of its funding comes from NNSA, the autonomous nuclear weapons organization within DOE. Therefore, despite the hype you hear from Livermore, it is not an energy project, or at least is not funded as such. If the National Ignition Facility, which is now operational, succeeds in achieving ignition and gain in the next couple of years, it will of course, have energy implications. Many very bright scientists believe in its energy potential. I don’t. The science is doable, but the engineering problems would make it too expensive using technology likely to be available in the near future. For one thing, you have to breed the tritium that an ICF reactor would use as fuel, because it doesn’t occur naturally. For that, you would have to build a complicated blanket or liquid curtain of lithium, which would produce tritium in reactions with fusion neutrons. The tritium would then have to be extracted. There are numerous other problems. However, as an above ground experimental facility for studying weapon physics and weapon effects, not to mention other aspects of high energy density physics and even astrophysics, the NIF would be an outstanding experimental tool – if it works. In fact, it would give us a good reason not to resume testing. By doing so, we would be throwing away a very significant advantage in the form of the NIF and other unique experimental facilities like Z at Sandia that no other country can match at the moment.

  19. George William Herbert (History)

    To amplify Helian’s answer –

    Yes, Booster bomb refers to limited fusion reactions enhancing the energy or explosive yield of a fission bomb (or, thermonuclear bomb’s “primary” first stage fission component).

    You do it by introducing small amounts of deuterium-tritium gas or lithium-deuteride solid into the fission bomb core; under typical conditions, a small amount of fusion happens when the fission bomb reaches around a quarter kiloton of fission yield. The energy release due to fusion is low, but there’s a very energetic neutron released in the fusion, which then rapidly and effectively causes a bunch more fission reactions to happen in the fission bomb components.